Electric projection lamp



Jan.

D. P. COOPER, JR ELECTRIC PROJECTICN LAMP Filed July 12, 1951' FIG. I

INVENTOR ATTORNEYS Patented Jan. 12, 1954 Emeral PROJECTION pester 'P. Cooper, J12, Cambridge, iMass,, assignor 'to Polaroid Corporation, Cambridge, Mass,, a

corporation of Delaware Application July 12, 1951 Serial No. 236,411 him- (01. 313-11 3) invention relates to electric lamps and similar devices "adapted to-project a beam ofiight in a predetermined direction and comprising an enclosure or bulb having an electrical energytranslation element or filament sealed therein and :a concave reflector so positioned as to.,sub-. stantially-collimate lightemitted by the filament.

:Qbjects ,of the inventlon'a-reto provide insuch a device a hat ribbon filament predeterminedly positionedwithrrespect to :the :focus of the refiector with the plane of the filament substantially parallel to 5th? direction :of propagation of light emitted by the device; "to provide a ribbon .filament, crimped or pleated throughout (its lightemitting portionlandwith the peaksiof the crimps or pleats substantially parallel .to eachother and either parallel with 'or perpendicular -to the long dimensionof'the filament; and to provide a'ribbon'filament ofthe charactendescribed so shaped the e ximumfi ame at r i ma tainedduring operation vof the lamp.- substantially to the-points ofcontactof the -ends-of the filament mith'the'lead-inwires.

Other objects of the invention will ,in part be obvious and will in part appear hereinafter.

The invention accordingly comprises an-article of manufacture possessing the features, properties, and relation of elements which will beex-v emplified in the article hereinafter described and thescope of theapplication of which will beindicated inthe claims.

Fora .fuller understandingof the nature and objects of .the invention, reference should be had torthe following detailed desorption takenin .con-

.nection with the'accompanying drawing wherein:

Figure l isa view in section of a light-projecting device comprising one form of the invention;

2 is a fragmentary view in elevation of theforward ends of the leadsand the ribbon filament of the device shown in Fig. 1;

Figs. 3 and 4 are views in elevation and plan of 1a crimped or pleated ribbon filament useful inthe'invention inwhich the pleatsextend perpendicularly'to the long dimension of the filamentpand :Flgs. Sande are views in.plan.and section of asimilarfilament wherein the pleatszextend parallel-to the long dimensionof the filament.

The "drawing illustrates a vehicle headlamp of-the ;sealed.-beam type which comprises" a, cup shaped base member In havingiits inner. surface l2 isilvered or otherwise coated'to provide ametallic .reflectonpreferably or paraboloidal shape. Theibasememberzhas hermetically sealed there,

to a transparent cover plate lilwof 1.g'lass rzwhich may :serve also as .-a :lens element for controllin the dispersion .of light emitted from the lamp. Within the bulb there is mounted a filament 1.6 on lead "wires Ill which, in turn, are mountedpn the base element 10 :in the usual ;ma.nner. TIE-he filament .is located accurately .at the focus of .the reflector t2 and maybe formed :of :any desired material such, iorexample, astungsten are high: melting .metallic [carbide .After assembly. :lthfi bulb is evacuated and may the filled "with anin: ert :gas ,or, :if :a high-me1ting :metafllic carbide is employed :as a filament, the bulb imay zbe allied with :an atmosphere comprising a volatile hydro:- carbon and hydrogen with-orzwithouteninertgas suohasargon.

The lam nlament YI-.6 isvribbonelike and either flat, :as shown in Fi s. :1. and 2, qrgcorrugated, pleat d r orimnod, as shown in Figsfito 16 in.- clusive. In every .caset efilamentispos' cr ed and :held by h zloa s with its narrowest dim, ension (thickness erp nd cular to, 1 and its :broad dim s on (width paral el w h, the direction f prop ation aof alight emitted from thelamp. lftthezfilamentemployed, iaa: flatthinribbon, the lone axisofthe filament will [bet-positioned sperpendioularl-ywto athe "axis :of the 'refiectorwwiththe plane of :the ribbon filament coinciding with the plane defined. by thelong axis: ofithe' filamentand the axis ;of the. reflector.

With the filamentpositioned at the focus of thezreflector in the manner described, asubstane tiall-y greater-percentage of light emitted xbythe filament will the incident .11130113-1711058- areasxoi the reflector which are most.eflectiveincauslng ecollimationbf the beam projectedby the lampsthan wouldibe the case :wereabar orcoil filament employed. .-The 'nar-rowedges of the filament only, i. ae., the forwardly directed :narrow edge shown for example in Fig. 2 of theLd-I-aWingand the corresponding rearwardly directed narrow-edge, emit light'which is directed either through the transparent cover plate of :the lamp without i-ncidence 'upon the eiiectiveareas 0 the -reflector "or wrearwar'dly toward those portions "of the 1 reflectorwhich for onereason or' another do'not collimate the light rays well forexample either because ofthe diiiicultyorproperly shaping the reflector or because 'the leads and lead mountingsinterfere. As a result, a greater percentage ofnusefulradiation is obtained in the collimatd beam Troma fiat ribbon filament mounted in'the manner described than from -a coil orbar -=filament. Where the tota1 radiant outputof a-coil or. bar' filament is the sameas'that of afiat-ribbon filament positioned in l the manner" described, the

flat ribbon filament is approximately from 25% to 30% more efiicient than is the coil or bar filament.

Preferably, the ribbon filament should be maintained as thin as practicable. For example, ribbon filaments of the order of .0025 inch in thickness, .030 inch in width and .375 inch in length between leads have proved completely satisfactory.

A modified form of ribbon filament for use in the invention is shown in Figs. 3 and 4. Here, the filament 30 is pleated, crimped or corrugated with the pleats running crosswise of the filament, i. e., parallel to the axis of the reflector when the filament is positioned in the manner heretofore described in connection with the filament shown in Figs. 1 and 2. Crimping the filament in this way causes it to approach more nearly a black body in appearance, 1. e., the surface brightness approaches more nearly that of a material with emissivity equal to unity. As compared to a flat filament, the loss of energy by convection from the crimped filament will increase, but less rapidly than the radiation loss, resulting in an increase in the luminous efficiency of the filament. Attention should be called to the fact that unless care is taken to make the crimp fine and uniform and with the distance between successive peaks as small as possible, portions of the filament, for example the peaks of the crimp, may lose heat at a different rate from other portions of the filament, for example the side walls of the crimp. Under these circumstances, the filament must be operated at a temperature lower than the maximum permissible temperature with a corresponding loss in luminous efficiency. This can be avoided by so crimping or corrugating the filament that the crimps are fine, i. e., adjacent peaks 32 are close together. More particularly, the distance between adjacent peaks 32 should be less than the width of the filament 3t and also less than the depth of the pleats.

The crimp depth should preferably be as great as possible consonant with the maintenance of substantially uniform temperature over all portions of the filament. For filaments of the character described, this means that the crimp depth may approximate or be slightly less than the filament width. A sharp bend at the peak of each crimp, as shown for example in Fig. 3, rather than a round bend is to be desired. Not only will all portions ofthe filament operate at more nearly the same temperature, but the sharp bend raises the effective emissivity of the element by reinforcing the actual emission with a reflected view of some other filament area. It will be apparent that pleating the filament will result in effectively reducing the distance between the leads.

In Figs. 5 and 6 there is shown a still further modification of the invention wherein the filament 40 is crimped or pleated with the peaks of the pleats 42 running lengthwise of the long dimension of the filament, i. e., perpendicular to the axis of the reflector.

In all of the embodiments of the invention shown, the ribbon filaments are reduced in cross-sectional area abruptly as they approach the leads. This is shown most. clearly, for example, in Figs. 4 and 5 at 50. This reduction in cross-sectional area of the filament is for the purpose of keeping the filament ends in contact with the leads at the high temperature of the body of the filament, and tends to ofiset the temenvelope.

perature loss in the filament ends by convection to the cooler, heavier leads. Such a structure as is shown in the drawing is not essential to the practice of the invention but it improves the efiiciency of the filament by permitting operation of substantially the entire filament length between leads at the same high temperature.

It is to be understood that it is not essential to the practice of the invention that the collimating reflector be formed integrally with the lamp The filament may, for example, be contained in a small supplemental lamp which is so positioned with respect to the reflector that the filament lies substantially at the focus of the reflector with the plane of the filament substantially parallel to a plane defined by the axis of the reflector and a line perpendicular thereto. Thus, the reflector may not only be positioned within the lamp envelop but it may be positioned outside the lamp envelope and either aifixed to the outer surface of the lamp envelope or positioned outside the lamp envelope and wholly separate therefrom. In this latter case the refiector may be protected by a second cover plate or it may be open and unprotected. All such modifications of structure are to be deemed within the scope of the invention. Moreover, while the reflector has been described as paraboloidal in shape and as a collimating reflector, and while it is believed that such a reflector will be found most useful in the practice of the invention, it is to be understood that the invention is ap-' plicable to a device employing a concave reflector which is substantially a surface of revolution and which has a focus, even though it does not fully collimate a beam of light.

As has already been pointed out, the filament of the invention may be formed of any suitable material, such as tungsten, osmium or tantalum, or under certain circumstances, and where the lamp is to be operated at high temperatures, it may be formed of a high-melting metallic carbide such as tantalum carbide, columbium carbide or zirconium carbide.

It will be understood, moreover, that the invention is applicable to lamps producing infrared or other nonvisible radiation as well as to lamps producing visible radiation.

The use of the word luminant or filament throughout the specification and claims is to be understood as including a radiation emissive element whether employed in connection with the emission of visible or invisible radiation.

Since other changes may be made in the above article without departing from the scope of the invention herein involved, it is intended that all matter contained in the above description or shown in the accompanying drawing shall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A radiation projecting device comprising a concave metal reflector which is substantially a' surface of revolution and which has a focus, an hermetically sealed light-transmitting envelope, a crimped ribbon filament mounted in said envelope, the peaks of adjacent crimps being substantially parallel and closely adjacent with the crimp depth greater than the distance between adjacent peaks, and means positioning said filament substantially at the focus of said reflector with the long axis of said filament perpendicular to the axis of said reflector and the broad dimension of said filament parallel to the plane defined by said axes.

2. A device as claimed in claim 1 wherein the filament has a width-to-thickness ratio of the order of 10 to 1.

3. A device as in claim 1 wherein the filament is crimped with the peaks of adjacent crimps spaced from one another by an amount less than the width of the filament.

4. A device as in claim 3 wherein the peaks of the crimps are parallel to the reflector axis.

5. A device as in claim 1 wherein the filament is sharply crimped with the crimps parallel to the long axis of the filament.

DEXTER P. COOPER, JR.

6 References Cited in the file of this patent UNITED STATES PATENTS Number Name Date Keyes Nov. 28, 1916 Pirani Aug. 27, 1929 Foulke Apr. 7, 1931 Barkey June 14, 1932 Wright Apr. 22, 1947 Plagge Mar. 22, 1949 Eaton Aug. 16, 1949 Stone Feb. 14, 1950 

